In order to position, retain, or hold absorbent cores such as those in disposable absorbent articles the core has been adhered or glued in place. One method deposits an adhesive or glue-type material onto a backing sheet whereon the absorbent core is positioned and thereby fixed in a spacial relationship to the other portions of the absorbent article. As the absorbent core is positioned in contact with the adhesive, the fibers which are on the surface of the core and thereby in contact with the adhesive thus are permanently attached to the backing sheet or the layers and remain fixed relative thereto. However, since the core typically is formed of fluffed cellulose or other absorbent fibers and the individual fibers are not adhered to each other in any way, only those fibers contacted specifically by the adhesive and thus fixed in their position are confined against undesired movement if or whenever the article and core receive moisture. The remainder of the core is free to move or separate.
A significant problem with any absorbent article occurs because the fibers of the absorbent core tend to shift and pull apart and the absorbent core loses its integrity should the absorbent core become wet and/or forces are exerted against it. Forces typically come from the wearer or user of the article due to normal movement in activities such as walking, bending, sleeping or sitting.
With the loss of the integrity of this core, the capability of the absorbent core to absorb and hold fluids is significantly degraded.
The fibers tend to separate if wet and when engaged by forces; thus, gaps in the absorbent core may form and permit the accumulation of fluids in that region without adequate absorbency to accommodate the fluid quantity.
Even though absorbent cores heretofore have been enclosed within an envelope of material, typically pervious to liquids on at least one side, the absorbent core contained therein may and can lose its structural integrity when wet.
According to this invention, the integrity of the fiber absorbent core is maintained even when wet by limiting displacement of the fibers in this core. A plurality of columns inserted into the absorbent fiber core or pad limits or restricts the movement of the core. The columns restrict movement of the fibers engaged by the columns to a very short distance, that between adjacent columns. Thus the columns will not only resist movement and core separation but also act to maintain a fairly even distribution of fibers and, therefore, fairly uniform absorbency. The columns preferably are formed on a backing sheet of a material impervious to liquids. The columns also may be formed on a top sheet, the top sheet being positioned next to the user or wearer of the article. The top sheet column would be projecting away from the user or wearer.
The columns are preferably formed by a process known as gravure printing. The polymeric material used to form the columns is typically polyethylene for use on polyethylene sheets or polypropylene for use on polypropylene sheets. The polymeric material is heated to the glass transition temperature of the material, Tg, and transformed into a softened and semi-liquid mass which then is deposited into cells or apertures on a gravure printing drum. The drum is rotated into face-to-face engagement with the sheet upon which the columns are to be formed and the softened or semi-molten material is contacted with the supporting sheet. As the supporting sheet is thereafter separated from the gravure printing drum or plate, the softened material will tend to string or pull out into an elongated form prior to cooling below its glass transition temperature, Tg. As the material is pulled out or strung into a plurality of vertical prongs and subsequently hardens, the prongs then are cut with the hot wire. It is important that the hot wire be disposed at a position which allows stretching of the material to occur prior to the material being severed, thereby leaving a series of columns protruding from the support sheet. Prophetically, excess height of the columns could be trimmed away by means of mechanical cutters and trimmers or by means of a hot wire which extends transverse to the sheet, at a height to allow the desired column height.
The gravure printing roll is maintained in a substantially one-to-one velocity ratio with the backing sheet; and as the backing sheet is separated from the printing roll, the columns will be pulled substantially perpendicular to the backing sheet. Depending upon preference, the columns may be of any cross-sectional shapes such as circular, oval, round, rectangular or triangular. The base end of the column is deposited on and joined to the backing sheet, typically by fusing with the material of the backing sheet at the column/support sheet interface as the heat softens the backing sheet.
The distal end of the column also may be of various configurations. Typical configurations may include a bulbous end, a hooked end, or sheared to form a pile from the columns otherwise cut off at a desired height. All of the above type terminations of the distal end are suitable as are any other form or shape of the distal end which may be inserted into the fiber mass of the absorbent core.
The absorbent core itself typically is a fluffed mass of cellulose fibers but it should be understood that it may be made of shredded foam or any other absorbent material. The fluffed core typically is deposited onto the support layer and pressed onto the columns formed on the support layer. As the columns penetrate and protrude into the absorbent core, they tend to limit the movement of the fibers of the absorbent core in a plane substantially parallel to the support layer. Movement of the fibers in directions corresponding to the axis of the projection is restricted by the construction of the absorbent article. A top sheet of liquid pervious sheet material may be provided with columns in a manner similar to or identical to that generally described above with the columns faced towards and projected into the fibrous absorbent core.
The top and backing sheets of the article then may be joined to form an envelope containing the absorbent core; if desired, attachment or fastening means for holding the article on the wearer in a position intended for both efficiency and comfort may be provided.
Significant and advantageous benefits resulting from the invention include improved wet integrity and improved uniformity of absorbency.